Underscore prefix on property name? [duplicate]

Question

Possible Duplicate:
How does an underscore in front of a variable in a cocoa objective-c class work?

Can anyone point me to an explanation of the use of underscores, I have always assumed that they are used to highlight that you are accessing the iVar [_window release]; rather than accessing the iVar via a setter/getter method [[self window] release]; or [self.window release]; I just want to verify that my understanding is correct.

@property (nonatomic, retain) IBOutlet UIWindow *window;
@property (nonatomic, retain) IBOutlet UILabel *markerLabel;

@synthesize window = _window;
@synthesize markerLabel = _markerLabel;

Answer 1

The use of an underscore for ivar names is a convention first used by Apple to differentiate between an actual ivar and a property. Many people have since adopted this convention.

The reason this is done is to prevent the mistake of assigning a new value to an ivar instead of to the actual setter:

myIvar = newValue;

instead of

self.myIvar = myValue;

If you accidentally use the top example, you could cause a memory leak. The underscore prevents you from making that mistake.